1. Field of the Invention
The present invention relates to a device and imaging system.
2. Description of the Related Art
Recently, MOS photoelectric conversion devices using MOS transistors as photoelectric conversion devices are being extensively developed. In these photoelectric conversion devices, the area of the light receiving surface of a photoelectric conversion portion (e.g., a photodiode) is decreasing as the pixel density increases and the downsizing of chips advances. Accordingly, the wiring material is being changed to copper more suitable to microfabrication than aluminum.
When using a copper interconnection, a diffusion protector for preventing the diffusion of copper is to be formed because the diffusion coefficient of a copper atom is large in an oxide film generally used as an interlayer insulator. A silicon nitride film is often used as a diffusion protector as an upper layer of a copper interconnection. A diffusion protector is used whenever the diffusion coefficient of the atom of a wiring material in an interlayer insulator is large, regardless of whether the wiring material is copper.
When using a diffusion protector in a photoelectric conversion device, a multilayered structure including an interlayer insulator and diffusion protector is formed. The refractive index of a film suitable for the diffusion protector, e.g., a silicon nitride film differs from that of a silicon oxide film used as the interlayer insulator. This mau pose a situation when the light amount entering the photoelectric conversion portion decreases owing to the influence of reflection or interference in the interface.
Japanese Patent Laid-Open No. 2005-311015 shows that diffusion protectors each have an opening corresponding to the light receiving region of a photodiode. Interlayers made of SiO2 are formed on the light receiving region of the photodiode, and a SiN protective film is formed on the interlayer. Japanese Patent Laid-Open No. 2005-311015 describes that the influence of reflection or multiple interference on the photodiode can be reduced because a region formed on the light receiving region of the photodiode is made of only a silicon oxide film having a single refractive index.
On the other hand, as the planar process techniques represented by photolithography and electron beam lithography advance, it becomes possible to form a micropattern having a dimension equal to or smaller than the visible light wavelength (subwavelength region) on the substrate surface. Accordingly, a condensing element (SubWaveLength Lens: SWLL) having the periodic structure of the subwavelength region is attracting attention. The “subwavelength region” is a region equal to or smaller than the wavelength of object light (visible light).
D. W. Prather (Opt. Eng. 38 870-878) describes that the research group of the Delaware University has proven by simulation that a lattice-like SWLL converted from a Fresnel lens as an aspherical lens has the condensing effect.
As described above, in the technique disclosed in Japanese Patent Laid-Open No. 2005-311015, the diffusion protectors each have the opening corresponding to the light receiving region of the photodiode.
Assume that the dimension of a pixel is decreased. In this case, the diffracting action of incident light at the opening end of each of the diffusion protectors reduces the ratio which the light reaching the light receiving surface of the photoelectric conversion portion accounts for in the light having entered the opening. That is, of the light having entered toward the photoelectric conversion portion, the ratio of light reaching the light receiving surface of the photoelectric conversion portion reduces. This decreases the sensitivity of the photoelectric conversion portion. The diffracting action of the incident light occurs not only at the opening end of the diffusion protector, but also at the interconnection opening end of an interconnection such as aluminum.